38 The process is repeated continuously and up to 120 layers can be created. Once complete, the battery manufacturer seals the edges of the foil. Afterwards, the cell stack is wrapped with foil, the foil is cut off and the remainder is secured with tape. Vacuum gripper systems pick up individual anode and cathode sheets, and alternately place them on the separator. Precise positioning of the electrode sheets and the separator is critical for the quality of this step. Edge alignment must be as accurate as possible, with tolerances in the µm range: deviations of less than 200 µm are acceptable. High speeds add to the challenge of this process step: the electrode sheets are picked up and placed on the cell stack in less than one second. Machine-vision systems, consisting of high-performance cameras and software, can ensure finished parts are produced correctly. In the inspection process, four cameras check the correct positioning of the electrode sheets at each corner. The CoaXPress 2.0 interconnect standard ensures precise triggering in multi-camera systems and real-time data transmission at speeds up to 12.5 Gbit/s. The captured image data can be analysed using software to determine the exact stacking of the electrode sheets. These vision systems need to be as compact as possible to fit into the production line and provide highresolution images for the analysis. Those tools ensure the measured distances are output in calibrated metrics, and compensate for radial and perspective distortions caused by camera settings. A model image can be used to define a measurement rectangle. During the process step, possible deviations in other acquired images of stacked anode and cathode sheets are output, either as coordinates if there is a rotation, or in metrics for distances to target edges to ensure stacking is within tolerance. Dry electrodes Solvent-free, or dry electrode, formulations are looking to avoid the issues of using toxic, expensive solvents that need to be recycled. Conventional coating of the electrode-collector foil requires low-viscous slurries with a solvent content of 45%. Subsequent solvent evaporation and recycling consumes the majority of energy, using 20% of the total required for cathode manufacturing, so reducing or eliminating the solvent in slurries could significantly improve the ecological and economic efficiency of electrode production. For solvent-free mixtures, special binders are necessary to produce cathode mixtures that can be calendared into cathode sheets and laminated onto current-collector foils. Polytetrafluoroethylene (PTFE) has been used for dry processing of conventional lithium-ion batteries, as well as solid-state batteries. PTFE, under certain processing conditions, can form fibrils interconnecting the cathode active material. Mixing such dry electrode formulations requires high-shear forces that conventional planetary mixers, traditionally used for wet electrode slurry mixing, cannot provide. Co-rotating, parallel, twin-screw extruders can apply greater shear force, generally adjustable via the screw design, and they have become very attractive for continuous, dry cathode mixing. For investigations of suitable cathode formulations and binder systems, a measuring mixer can be used to mix smaller amounts of samples in batches. Similar to a twin-screw extruder, measuring mixers with two co-rotating rotors can mix cathode material with PTFE to induce its fibrillation. From the dry cathode granulate, cathode sheets can be formed and laminated onto the current collector foil using calendars. The mixer, also called a torque rheometer, kneads and heats material January/February 2025 | E-Mobility Engineering Inline viscosity sensing for slurry (Image courtesy of Rheonics)
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